A distributed denial of service (DDoS) attack means an attack of making a specific web site unavailable or blocking services from being provided on the specific web site by controlling several tens to several hundreds of computers at a remote place to simultaneously access the specific web site so that the specific web site may be overloaded within a short time. In general, in order to block the DDoS attack, a network infrastructure for dispersing or absorbing a large amount of traffic is prepared, the amount of traffic to flow into a system, which is a target of attack, is controlled using IPS (Intrusion Protection System) equipment, well-known harmful packets are blocked, and harmful traffic is blocked by installing exclusive equipment at a front end of the system.
However, control personnel are indispensable to diverting and handling traffic in the middle of the above methods. Thus, the DDoS attack is difficult to block in real time and it is unavoidable that a service is discontinued at least once at first.
A client may establish one-to-one communication with a first server or a second server to be provided a desired service.
However, in such a service system, information regarding a server (e.g., an IP address) may be exposed when a client establishes one-to-one communication with the server. Thus, the service system may become a target of attack. To prevent this problem, a gateway or a proxy server may be installed to not expose information regarding the server (e.g., an IP address). However, in this case, the problems of the server may be a burden on the gateway or the proxy.